Have you ever just looked around at humans and realized that we look really, really, weird? Aside from horses we are pretty much the only species that has a huge concentration of hair in one particular spot. Sure, there are some furry people out there with a good amount of body hair, but why is it that we continuously grow so much hair and in such different varieties on top of our heads? Well evidently I was not the only person only ever wonder this and according to the New York Times the answer lays in first questioning why humans lost their body fur. As were evolved from primates the most obvious difference between us has got to be the fact that humans aren’t covered head to toe in thick fur. As it turns out we don’t exactly know why humans lost their fur but one of the most prevailing theories is that “Humans lost their body hair, they say, to free themselves of external parasites that infest fur — blood-sucking lice, fleas and ticks and the diseases they spread.” This would make sense in regards to survival of the fittest, those born with a mutated gene for less hair are less prone to sickness and pair off with others and pass on the beneficial gene and a few centuries later we have the “naked” man. But remember sexual selection plays a big factor in evolution and despite our desire for hairless bodies the attraction to those with a thick crop of hair atop the head prevailed.
But this still doesn’t exactly answer my question as to why we developed hair that is worn on top our heads in so many different fashions. So after some more extensive research on the different types of hair out there I found myself closer to what I was looking for. To begin with the reason we have hair on top of our heads is it provides the scalp insulation from the sun, blocks UV light exposure, and provides cooling when sweat evaporates from soaked hair. So that at least explains what it is doing there. But why does the texture and coarseness of hair vary so much in humans?
Beginning with color, pigmentation in humans is what determines the color of hair. Eumelanin is a pigment that results in darker hair colors such as dirty blond, brown, and black, while pheomelanin occurs in red hair. What about blonde hair you might ask? Well interestingly enough they have the same pigmentation as darker haired people they just have significantly less of it found inside the follicle. In regards to why there are so many different textures of hair scientists aren’t entirely sure but the main theory is that the shape of the hair shaft affect the curliness of the hair. Those with rounder shafts have straighter hair, while those with flatter more condensed hair shafts have curlier hair. So overall the way you become matched up with your specific hair color and type of hair is the same way you inherit any trait, through your genes. This is why curly haired people have curly haired children, because they are passing down the flatter hair shaft gene.
Now we all know that certain races have similar hair textures and the reason for that is pretty interesting. African American hair is primarily curly or kinky and this is due the intense UV light exposure in Africa, in which curly hair proved to be more beneficial in cooling and protecting the scalp from the sun. While in Asia where straight hair is the norm, there wasn’t enough intense heat to cause the need to evolve hair into curly formations and through sexual selection and evolution straight hair was found to be desirable and was passed down. Overall our hair is a very fascinating subject, one that science still has many different questions to answer.
Source:
http://www.nytimes.com/2003/08/19/science/why-humans-and-their-fur-parted-ways.html
http://en.wikipedia.org/wiki/Long_hair
http://www.hairlosshelp.com/hair_loss_research/hair.cfm
http://www.bio.davidson.edu/courses/genomics/2011/Piper/Background.html